HEIC1003: EMBARGOED UNTIL 16:00 (CET)/10:00 am EST 11 Feb, 2010
http://www.spacetelescope.org/news/html/heic1003.html
Photo release: Saturnís aurorae offer stunning double show
11-Feb 2010 Researchers using the NASA/ESA Hubble Space Telescope recently took
advantage of a rare opportunity to record Saturn when its rings are edge-on,
resulting in a unique movie featuring both of the giant planetís poles. Saturn is
only in this position every 15 years and this favourable orientation has allowed a
sustained study of Saturnís almost symmetric northern and southern lights.
An enormous and grand ringed planet, Saturn is certainly one of the most intriguing
bodies orbiting the Sun. Hubble has now taken a fresh look at the fluttering aurorae that
light up both of Saturnís poles.
It takes Saturn almost thirty years to orbit the Sun, with the opportunity to image both of
its poles occurring only twice in that period. Hubble has been snapping pictures of the
planet at different angles since the beginning of the mission in 1990, but 2009 brought a
unique chance for Hubble to image Saturn with the rings edge-on and both poles in view.
At the same time Saturn was approaching its equinox so both poles were equally
illuminated by the Sunís rays [1].
These recent observations go well beyond just a still image and have allowed researchers
to monitor the behaviour of both Saturnís poles in the same shot over a sustained period
of time. The movie they created from the data, collected over several days during January
and March 2009, has aided astronomers studying both Saturnís northern and southern
aurorae. Given the rarity of such an event, this new footage will likely be the last and best
equinox movie that Hubble captures of our planetary neighbour.
Despite its remoteness, the Sunís influence is still felt by Saturn. The Sun constantly
emits particles that reach all the planets of the Solar System as the solar wind. When this
electrically charged stream gets close to a planet with a magnetic field, like Saturn or the
Earth, the field traps the particles, bouncing them back and forth between its two poles. A
natural consequence of the shape of the planetís magnetic field, a series of invisible
ďtraffic lanesĒ exist between the two poles along which the electrically charged particles
are confined as they oscillate between the poles. The magnetic field is stronger at the
poles and the particles tend to concentrate there, where they interact with atoms in the
upper layers of the atmosphere, creating aurorae, the familiar glow that the inhabitants of
the Earthís polar regions know as the northern and southern lights.
At first glance the light show of Saturnís aurorae appears symmetric at the two poles.
However, analysing the new data in greater detail, astronomers have discovered some
subtle differences between the northern and southern aurorae, which reveal important
information about Saturnís magnetic field. The northern auroral oval is slightly smaller and
more intense than the southern one, implying that Saturnís magnetic field is not equally
distributed across the planet; it is slightly uneven and stronger in the north than the
south. As a result, the electrically charged particles in the north are accelerated to higher
energies as they are fired toward the atmosphere than those in the south. This confirms a
previous result obtained by the space probe Cassini, in orbit around the ringed planet
since 2004.
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Notes for editors
[1] The equinox identifies one of the two moments during a planetís journey around the
Sun when the light rays coming from the star are perpendicular to the planetís equator.
On Earth, we are familiar with the spring and autumn equinoxes, two special dates in the
calendar when day and night have the same length everywhere on the globe. Just like
equinoxes on Earth, which occur twice in a yearly orbit, Saturn also has two equinoxes per
orbit. However, Saturn takes almost 30 Earth years to orbit the Sun, thus experiencing an
equinox every 15 of our years.
The Hubble Space Telescope is a project of international cooperation between ESA and
NASA.
Image credit: NASA, ESA and Jonathan Nichols (University of Leicester)
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For more information, please contact
Colleen Sharkey
Hubble/ESA, Garching, Germany
Tel: +49-89-3200-6306
Cell: +49-015115373591
E-mail: csharkey@eso.org
Jonathan Nichols
University of Leicester
Physics and Astronomy Department
Tel: +44-116-252-5049
E-mail: jdn@ion.le.ac.uk